1. Field of the Invention
The present invention relates to a capillary for wire bonding, and in particular for wire bonding for semiconductor devices.
2. Description of the Related Art
Generally, a capillary is formed of a cone-shaped insulating material, and a hole through which a metal wire passes is provided within the capillary.
As shown in FIGS. 6A and 6B, this capillary comes in two types, that is, a normal capillary 100 and a bottleneck capillary 102. These capillaries are distinguished from each other based on the shape of the ends thereof.
The bottleneck capillary 102 is formed in such a manner that an end thereof is made narrow in the transverse direction by shaving off an end of the normal capillary 100. The length L1xe2x80x2 of a face surface 102A by which compression bonding portions 106 and 108 of a metal wire 104 (see FIGS. 7A and 7B) are formed, is shorter than the length L2xe2x80x2 of a face surface 100A of the normal capillary 100.
FIG. 8 and FIGS. 9A and 9B each show a wire bonding method using the normal capillary 100. In this wire bonding method, bead bonding is employed, in which the metal wire 104 is discharged and melted by an electric torch (not shown in the drawings) and a ball (not shown in the drawings), which will be hereinafter referred to as a xe2x80x9cbeadxe2x80x9d, is formed at an end of the metal wire 104.
The bead thus formed is compressively bonded onto an electrode pad 110 by the face surface 100A of the normal capillary 100, and a compression bonding portion 112 is formed. The compression bonding portion 112 allows one end of the metal wire 104 to be joined to the electrode pad 110 on a semiconductor element 101.
The other end of the metal wire 104 is compressively bonded by the face surface 100A of the normal capillary 100 onto a post portion 116 connected to an external electrode of a semiconductor device 114, and a compression bonding portion 118 is formed. The compression bonding portion 118 allows the other end of the metal wire 104 to be joined to the post portion 116.
In such a manner as described above, the electrode pad 110 and the post portion 116 are connected by the metal wire 104. Subsequently, the metal wire 104 is cut off on the compression bonding portion 118 and wiring between the electrode pad 110 and the post portion 116 is thereby completed.
On the other hand, FIGS. 7A and 7B show a wire bonding method using the bottleneck capillary 102.
The length L1xe2x80x2 of the face surface 102A in the bottleneck capillary 102 is shorter than that in the normal capillary 100. Therefore, the respective areas of the compression bonding portions 106 and 108 formed at the time of wire bonding are each made smaller.
When the semiconductor element 101 (see FIG. 8) is of small size and the pitch between electrode pads 120 is short, bonding is not possible in the normal capillary 100. Therefore, the bottleneck capillary 102 is used. However, in the bottleneck capillary 102, the area of the compression bonding portion 108 formed on a post portion 122 is also small, and therefore, bonding strength of the post portion 122 decreases.
Further, minuteness of the semiconductor element 101 and reduction in the pitch between the electrode pads 120 have been demanded in recent years, and it is necessary that the face surface 102A of the bottleneck capillary 102 be reduced in length. Therefore, the area of the compression bonding portion 108 further becomes smaller, and it is difficult to maintain the bonding strength of the post portion 122.
As a result, when the semiconductor device 114 has a multi-pin structure and is formed as a large-sized package due to a tendency toward the minuteness and a multifunctional structure of the semiconductor element 101, a stress acting on the compression bonding portion 108 of the post portion 122 becomes larger at the time of resin-sealing of the semiconductor element 101. Accordingly, it is difficult for the area of the compression bonding portion 108 in the bottleneck capillary 102 in the present state to withstand a stress acting at the time of resin-sealing for the semiconductor element 101.
In view of the above-described circumstances, it is an object of the present invention to provide a capillary which prevents an electrode pad of a micro-sized and multifunctional semiconductor element from contacting an adjacent wire previously subjected to wiring and which allows the area of a compression bonding region in a post portion to increase.
In a first aspect of the present invention, there is provided a capillary used for wire bonding, wherein a compression bonding area formed when a metal wire is bonded onto a post portion to be connected to an electrode pad formed on a semiconductor element is made larger than a compression bonding area formed when the metal wire is bonded onto the electrode pad.
Thus, the respective compression bonding areas in the electrode pad and in the post portion can be changed appropriately. Therefore, even when the semiconductor element is of small size and the pitch between electrode pads is short, the compression bonding area on the post portion can be increased.
As a result, the bonding strength of the post portion increases. Even if the semiconductor device has a multi-pin structure and is formed as a large-sized package, the post portion can withstand a stress acting thereon at the time of resin-sealing for the semiconductor element.
In a second aspect of the present invention, there is provided a semiconductor device in which a pitch between post portions respectively connected to electrode pads formed on a semiconductor element is made greater than a pitch between the electrode pads, and a compression bonding area formed when a metal wire is bonded onto the post portion is larger than a compression bonding area formed when the metal wire is bonded onto the electrode pad.
The pitch between the post portions is made greater than the pitch between electrode pads. Therefore, even if the compression bonding area formed by bonding for the post portion is made larger than the compression bonding area formed by bonding for the electrode pad, short circuits do not occur between the post portions.
In a third aspect of the present invention, an accommodating portion is provided at an end of the capillary main body, and a movable portion through which a wire passes is accommodated in the accommodating portion. The movable portion slides to protrude from the end of the capillary main body, wherein further movement in this direction is prevented. Further, urging means is accommodated in the accommodating portion and urges the movable portion toward the end of the capillary main body.
When a metal wire is bonded onto the electrode pad formed on the semiconductor element, a molten metal wire is compressively bonded by the movable portion using pressing means. Further, when the metal wire is bonded onto a post portion to be connected to the electrode pad, the metal wire is compressively bonded by the movable portion and the end of the capillary main body, using the pressing means.
So long as the movable portion is thus made to slide, when bonding is carried out for the electrode pad, the metal wire can be compressively bonded only by the movable portion. Further, when bonding is carried out for the post portion, the metal wire can be compressively bonded by the end of the capillary main body and the movable portion acting together.
As a result, respective functions of a normal capillary and a bottleneck capillary can be provided by a single capillary. Moreover, the compression bonding area in the post portion can be easily made larger than the compression bonding area in the electrode pad.
In a fourth aspect of the present invention, the accommodating portion includes an inner peripheral surface having a groove defined therein and extending in a direction that the movable portion slides, and the movable portion including an outer peripheral surface having a projection extending into the groove and sliding therein as the movable portion slides.
Accordingly, the projection formed in the movable portion is engaged with the groove formed along a direction in which the movable portion slides. Therefore, the movable portion is substantially prevented from rotating, although it slides. As a result, there is reduced risk that a compression bonding portion or the like will be displaced at the time of bonding for the post portion.
In a fifth aspect of the present invention, the movable portion and the capillary main body each include an end surface, and a stopper is provided in the groove at a location preventing further movement of the projection and the movable portion when the end surfaces substantially align with one another.
Thus, sliding movement of the movable portion is regulated at the position where the end surface of the movable portion and the end face of the end of the capillary main body are placed on substantially the same plane. Therefore, bonding is carried out for the post portion in the state in which the length of the face surface is effectively of the transverse dimension of the end surface of the movable portion and of the end face of the end of the capillary main body together.
In a sixth aspect of the present invention, a fixed body through which a wire passes is provided in a core portion of a capillary main body. The fixed body protrudes from the end of the capillary main body.
An annular hollow portion is provided between the fixed body and the capillary main body. The hollow portion is sealed substantially airtight by a moving body. The moving body slides while maintaining a substantially sealed state and protrudes from the end of the capillary main body, whereupon further movement in the protruding direction is prevented.
Additionally, air can be supplied into and exhausted from the hollow portion by an air supply/exhaust opening. The hollow portion includes tension means accommodated therein, and the tension means retracts the moving body back into the hollow portion.
When the metal wire is bonded onto the electrode pad formed on a semiconductor element, a molten metal wire is compressively bonded by the fixed body when air is exhausted from the air supply/exhaust opening and the moving body is retracted into the hollow portion by the tension means.
When the metal wire is bonded onto a post portion to be connected to the electrode pad, the metal wire is compressively bonded by the fixed body and the moving body protruding from the end of the capillary main body due to pressure of air supplied from the air supply/exhaust opening.
In a seventh aspect of the present invention, the hollow portion includes an inner peripheral surface having an engagement groove defined therein and extending in a direction in which the moving body slides, and the moving body includes an outer peripheral surface having an engaging portion disposed slidably in the engagement groove and sliding therein as the moving body slides.
In an eighth aspect of the present invention, the moving body and the fixed body each include an surface, and an engagement stopper is provided in the engagement groove and regulates movement of the engaging portion so that the end surfaces substantially align with one another.
Accordingly, movement of the engaging portion is not only regulated by the engagement stopper at the position where the end surface of the moving body and the end surface of the fixed body are placed on substantially the same plane, but it is also unnecessary to separately provide a removal-preventing stopper for retaining the moving body within the capillary main body.